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Projects => Diode-Compression Op Amp => Topic started by: blackcorvo on October 11, 2012, 02:14:35 PM

Title: Diode Compression Power Amp?
Post by: blackcorvo on October 11, 2012, 02:14:35 PM
I know there is a project for a power-amp using the diode-compression trick, but I wanted to know if you could use that in low-power amps (under 10w) to obtain the same effect?
I'm looking for a practice amp I can carry around easily, and maybe power it with a 12v 7.5Ah sealed battery.
Title: Re: Diode Compression Power Amp?
Post by: Jdansti on October 11, 2012, 03:38:27 PM
It wouldn't be diode compression, but the Tiny Giant amp (20W) is a good one that runs on 12V. If you want under 10W, substitute a TDA2003 for the TDA7240A.
Title: Re: Diode Compression Power Amp?
Post by: psychedelicfish on December 24, 2012, 12:03:04 AM
For a low powered battery amp, you could make this: http://sound.westhost.com/project113.htm, replacing the op amp with the diode compressor. As it says on the page, you could get 1.5W into 8 ohms, though probably less with a battery. You would probably have make a voltage divider across the battery, and use the middle of the divider as ground. If you want more power, you might be able to use a dc wall adapter to power it and replace the power transistors with some that have a bit more grunt.
Title: Re: Diode Compression Power Amp?
Post by: blackcorvo on July 01, 2013, 03:50:41 AM
Hey, I'm back on this subject yet again.

psychedelicfish, I was really looking for something with at least 5 watts, but that circuit seems interesting. Another one I found that is quite similar (but more powerful) is the following:

http://www.redcircuits.com/Page164.htm

However, a couple days ago I was looking at some old circuit boards I have in a box (which I use for recycling still-usable components), and in one of them there's a TEA2025 stereo power-amp, which gives around 2.5w per channel in stereo, and a little under 5w in mono (bridge). Also, it works from 3v up to 12v.

I haven't had much luck with chip power-amps in the past (they either distort horribly with a small signal, or they oscillate at full volume), but I might give this little guy a try. Seems simple enough, and I already prepared a layout in DIY Layout Creator (first layout I've done in a couple years, and I believe it looks decent):

http://img208.imageshack.us/img208/7305/5id.png

Still, I'm interested in trying the discrete op-amp + power transistors approach sometime in the future, specially because I could try using high-voltage transistors for the op-amp (MPSA92 for the PNPs and MPSA42 for the NPN), and I wouldn't have to worry about frying them anytime soon (and since these are low-gain ones, they might give a nice drive sound when pushed hard by a loud preamp).
Title: Re: Diode Compression Power Amp?
Post by: blackcorvo on May 16, 2014, 02:05:32 PM
So, after looking around for discrete amplifiers that might suit this idea, I stumbled upon this sort of push-pull design:

(http://www.hilberink.nl/amps/2n3055amp1.gif) (http://www.hilberink.nl/amps/2n3055amp2.gif)

Taking a good look at them, I decided to see if I could insert the Diode Compression Op-Amp somewhere in there and make it part of the power-amp.
So, after succesfully sticking the DCOA in there, and a lot of changing values of stuff over and over again, here's the result I ended up with:

ATTENTION! NOT TESTED!

(http://24.media.tumblr.com/a69511ca47fd20de7d41567fe1d64482/tumblr_n5ohem7xKb1r4gqjso1_r1_1280.png)

I'm no engineer and I barely understand how to polarize a simple transistor booster, so I have no idea if this is even gonna work IRL. Most of the stuff I've built in Livewire worked in the breadboard afterwards, but you never know.
Title: Re: Diode Compression Power Amp?
Post by: tca on May 17, 2014, 05:32:21 PM
I know there is a project for a power-amp using the diode-compression trick...
What trick is that? Which power amp?
Title: Re: Diode Compression Power Amp?
Post by: blackcorvo on May 17, 2014, 07:05:34 PM
I know there is a project for a power-amp using the diode-compression trick...
What trick is that? Which power amp?

The trick I speak of is soft clipping as the power amp overdrives, and the project I was mentioning there is Joe Davisson's Diode Compression Amplifier (http://www.diystompboxes.com/analogalchemy/sch/diodepwr.html). Only "problem" with that project is the power output (which is 100 watts IIRC) is way too much for me.

I play at home, just for fun, so anything in the range of 1w-5w would be ideal.

I know they have mentioned the Tiny Giant before, but I just really wanted to try getting a decent overdriven sound from the power amp.
Title: Re: Diode Compression Power Amp?
Post by: Joe on May 22, 2015, 12:33:23 AM
I'm sorry to get to this so late.

The "diode-compression" power amp I posted worked but had biasing issues. So I'm using it without the diode tricks now. (Having run the amplifier in both modes, I came to realize that Bruce DePalma's design sounds *superb* as a guitar amp on it's own anyway.)

For smaller amps I think blackcorvo's concept seems doable, gonna play around with it in the coming weeks.